Prostaglandins modulate platelet aggregation, kidney function, immune responses, respiratory function, reproduction and other physiological processes. Abnormalities of prostaglandin biosynthesis occur in pain, fever, bone resorption, cardiovascular disease, inflammation and cancer. Cyclooxygenase/prostaglandin synthase (COX/PGS) catalyzes the synthesis of the common intermediate, PGH2, in the production of prostaglandins. We identified a second, inducible COX, COX-2. We also demonstrated that COX-2 induction is required for prostaglandin production in response to growth factors and inflammatory stimuli, a result that provides the rationale for the clinical utility of COX-2 specific inhibitors. Elevated COX-2 gene expression plays a role in many pathologies. The ability to measure COX-2 expression in living animals would permit us to (i) determine the role of COX-2 in inflammatory responses and tumor progression and (ii) evaluate the utility of monitoring COX-2 expression as an intermediary marker of both disease and therapeutic response. We developed methods to measure reporter gene expression repetitively, non-invasively and quantitatively in living animals. We express reporter genes whose protein products sequester positron-labeled probes, then detect reporter gene-dependent probe retention by using positron emission tomography (PET). We have developed two systems; (i) Herpes Simplex Virus 1 thymidine kinase (HSV1-tk) as the "PET reporter gene" and [18F]-8-acycloguanosines (ganciclovir, penciclovir) as the "PET reporter probes", and (ii) the dopamine D2 receptor (D2R) as the PET reporter gene and [18F] fluoroethylspiperone as the PET reporter probe. We validated these two PET reporter gene systems in both a somatic viral delivery model and in transplantable tumor models. We will develop procedures to quantitatively and non-invasively monitor PET reporter gene expression from COX-2 promoter-driven transgenes and from the endogenous COX-2 gene. We will create transgenic and "knock-in" mice in which the HSV1-tk and D2R PET reporter probes to monitor COX-2 gene expression in four inflammation models (the carageenan-injected paw, air-pouch inflammation and liver inflammation) and in two tumor induction systems [multi-stage initiation-promotion- progression skin carcinogenesis and intestinal neoplasia in min1(+/- )mice]. These mice will permit investigators to monitor COX-2 expression in a variety of paradigms.